JackBean wrote:it should be isotonic, otherwise there would be flow of water either inside or outside

How can it be isotonic when there is a big difference between vacuole's and cytoplasm's consistency?!In my point of view it's hypotonic to the cytoplasm but tonoplast that is around of the vacuole ,doesn't allow to the water to enter to the cytoplasm.

The most difficult step is first step.Cyrus The Great ,Most powerful and well known Iranian emperor

Adz795 wrote:I don't get the consistency issues. What do you mean? Is there a difference in the viscosity of vacuolar and cytosolic fluids? How consequence does that have?

If we name water's volum in vacuole-cytoplasm "a"-"b" and total volume of vacuole-cytoplasm "c"-"d";a/c>b/d ;So we say water consistency of vacuole is higher than cytoplasm.

As a result we can say the Vacuole is hypotonic to the cell.but tonoplast usually doesn't allow to the water to enter to the cytoplasm. (vacuole's tonoplast has an attribute named "selective permeability" cause it)I hope you had got what I mean.

The most difficult step is first step.Cyrus The Great ,Most powerful and well known Iranian emperor

Yes, I got what you wanted to say. What you explained simply meant that the vacuole has more water/volume than the cytoplasm. Thanks for that. From this I may suspect that the tonoplast is not just any lipid bilayer and that it is is more adept at handling tonicity than the plasma membrane.

Adz795 wrote:Yes, I got what you wanted to say. What you explained simply meant that the vacuole has more water/volume than the cytoplasm. Thanks for that. From this I may suspect that the tonoplast is not just any lipid bilayer and that it is is more adept at handling tonicity than the plasma membrane.

Exactly.it's membrane contains protein.

The most difficult step is first step.Cyrus The Great ,Most powerful and well known Iranian emperor